1. Field of the Invention
The present invention relates to a process for the preparation of derivatives of perfluoroalkane-carboxylic acids (R.sub.F COOH) and perfluoroalkane-sulphinic acids (R.sub.F SO.sub.2 H), in which R.sub.F represents a perfluorinated branched or unbranched C.sub.n F.sub.2n+1 radical containing from 2 to 12 carbon atoms.
2. Description of the Prior Art
The prior art has disclosed various methods for preparation of derivatives similar to those presently disclosed. For example, it has been disclosed, hitherto, that these products may be prepared by electrofluorination, such as described in J. Chem. Soc. (1956), p. 173, in U.S. Pat. No. 2,732,398 and in Ind. Eng. Chem. (1951) 43 2332. Nevertheless, this technique is difficult to apply in practice and in the case of heavy acids, the method is characterized with very poor yields.
Chemical methods for obtaining these compounds have also been described, such as those comprising a reaction involving introduction of CO.sub.2 (J. Fluorine Chem. 1974 3 247) and of SO.sub.2 (J. Fluorine Chem. 1975 5 265) in perfluorinated magnesium compounds. This technique is very difficult to apply and in particular requires a reaction temperature of the order of -40.degree. C. to -70.degree. C.
The same derivatives can also be obtained according to the teachings of French Patent Application No. 76/06303 and its Certificate of Addition No. 76/37240 whereby perfluoroalkyl halides are reacted with CO.sub.2 or SO.sub.2 in a dimethyl sulphoxide medium and in the presence of a metallic pair, particularly the pair zinc-copper.
It has now been found that by practice of the present invention, there is provided a new process for the preparation of these derivative products, which consists in reacting perfluoroalkyl halides with CO.sub.2 or SO.sub.2 in a solvent medium and in the presence of zinc. The reactivity of these perfluoroalkyl halides with SO.sub.2 and with CO.sub.2 in the presence of zinc is quite unexpected, because from the literature (J. Chem. Soc. 1953 p. 3607 and J.A.C.S. 1957 75 p. 4159), it is known that perfluoroalkyl iodides react in a solvent medium with zinnc to give organozinc derivatives R.sub.F Zn I which are only very slightly reactive and in particular do not react either with CO.sub.2 or with SO.sub.2.